Axial field motor/generator

ABSTRACT

An axial field motor/generator having a rotor that includes at least three annular discs magnetized to provide multiple sector-shaped poles. Each sector has a polarity opposite that of an adjacent sector, and each sector is polarized through the thickness of the disc. The poles of each magnet are aligned with opposite poles of each adjacent magnet. Metal members adjacent the outermost two magnets contain the flux. The motor/generator also has a stator that includes a stator assembly between each two adjacent magnets. Each stator assembly includes one or more conductors or windings. Although the conductors may be formed of wire having a round, uniform cross-section, they may alternatively be formed of conductors having a tapered cross-section that corresponds to the taper of the sectors in order to maximize the density of the conductor in the gap between axially adjacent poles. The conductors may also alternatively be formed of traces in a printed circuit, which may have one or more layers. Each stator assembly may be removably connectable to another stator assembly to provide modularity in manufacturing and to facilitate selection of the voltage at which the motor/generator is to operate. Electrical contacts, such as pins extending from the casing, may removably connect the conductors of adjacent stator assemblies. A magnet may be dynamically balanced on the shaft by hardening a thin ring of cross-linked resin between the magnet and the shaft while the shaft is spun, using ultraviolet light to polymerize the resin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electric motor/generatorsand, more specifically, to a permanent magnet, axial fieldmotor/generator.

2. Description of the Related Art

An electric motor, which is a machine for converting current intomotion, typically includes a rotor that rotates within a stator inresponse to a magnetic field. In a permanent magnet motor, the rotor orstator, typically the stator, includes one or more permanent magnetsthat generate a magnetic field. Permanent magnets may be made of ferrousmetals or ferroceramic materials. Because the machine may also be usedto convert motion into electric current, the machine is often referredto in the art as a motor/generator or a dynamo. Therefore, although theterm "motor" is used herein for convenience, it should be understoodthat the same machine may be used as a generator.

The rotor or stator of a permanent magnet motor, typically the rotor,includes conductors, such as copper wire, wound around a form. Thesewindings typically have numerous turns of the wire in order to maximizethe magnitude of the magnetic field.

In certain permanent magnet motors, the stator includes a metal casingthat holds two or more magnets and completes the magnetic circuitbetween them. The casing typically comprises metal plates or laminationsto minimize eddy currents. Increasing the amount of metal in the casinglowers the reluctance of the circuit, thereby increasing the proportionof magnetic flux in the gaps between the magnet poles through which therotor windings move.

Common motor magnet materials include iron, an aluminum-nickel-cobaltalloy known as Alnico, and rare-earth materials, such as asamarium-cobalt alloy. These materials provide a strong magnetic fieldbut are quite heavy.

Motor magnets commonly must be magnetized in-place, i.e., after theyhave been assembled into the metal motor casing, to minimizedemagnetization upon assembly. If a magnet is removed from the casing(or inserted into it), the act of removing (or inserting) it generallydemagnetizes it to some extent. Replacing the magnet would result indiminished performance. To minimize demagnetization, a metal "keeper"may temporarily be attached to a magnet prior to mounting it in a motoror other device.

Practitioners in the art have developed axial field motors havingmagnets disposed on a rotor with their fields aligned parallel to theaxis of rotation of the motor. Axial field motors do not require heavymetal casings to contain the field. Practitioners in the art havedeveloped small axial field motors that include economical ferroceramicmagnets. Unlike rare earth magnets, ferroceramic magnets can readily bemagnetized into multiple poles because they have a relative permeability("μ") on the order of 1. (Permeability is defined as the ratio betweenthe magnetic field density (B) of a material to its magnetic fieldintensity (H). Air, by definition, has a relative permeability of 1.) Incertain such motors, each rotor disc is magnetized into multiplesector-shaped poles. Each sector has a polarity opposite that of anadjacent sector, and each sector is polarized through the thickness ofthe disc. The rotor is disposed adjacent to the stator on a common axis.The stator of such a motor typically consists of multiple toroidalwindings. The magnetic field through which the windings pass isconcentrated between two adjacent sectors of the same disc.

Motors having ferroceramic magnets produce lower torque than motorshaving magnets made of high-permeability materials, such as iron, Alnicoand rare earth materials, because ferroceramic magnets exhibit a lowerflux density. To obtain an increase in torque, the rotor may have twodisc magnets, one on each side of the stator. Half of each toroidalwinding of the stator thus passes through the magnetic field generatedby one magnet of the rotor, and the other half of the winding passesthrough the magnetic field generated by the other rotor magnet.Nevertheless, the density of the flux through which each winding halfmoves is limited to that produced by the disc magnet to which it isclosest. The use of multiple pole ferroceramic magnets is thereforelargely confined to small, low-torque motors, such as stepper-typemotors used in disk drives.

It would be desirable to provide an economical motor that has a highpower-to-weight or efficiency ratio. These needs are clearly expressedin the art and are satisfied by the present invention in the mannerdescribed below.

SUMMARY OF THE INVENTION

The present invention pertains to an axial field motor/generator havinga rotor that includes at least three annular discs magnetized to providemultiple sector-shaped poles. Each sector has a polarity opposite thatof an adjacent sector, and each sector is polarized through thethickness of the disc. These magnets may be made of any suitable,relatively low magnetic permeability ("μ") material, such as aferroceramic material having a permeability of no more than about 100times the permeability of air. The poles of each magnet are aligned withopposite poles of each adjacent magnet. The magnetic flux thus isoriented axially through aligned sectors of adjacent magnets. Metalmembers adjacent to the outermost two magnets contain the flux in therotor. Thus, conceptually, the flux follows a circular serpentine paththrough and around the rotor.

The magnets are polarized into a plurality of sectors, which minimizesdemagnetization prior to assembly of the rotor. Thus, the magnets neednot be magnetized in-place, i.e., after assembly, as in certainconventional motors. Moreover, it is not necessary to use a keeper toolto maintain magnetization during assembly.

The motor/generator also has a stator that includes a layer ofconductors or windings between each two adjacent rotor magnets. Eachlayer may have multiple conductor phase assemblies, each providing oneof a plurality of phases. Although the conductors may be formed ofconventional wire having a round, uniform cross-section, they mayalternatively be formed of conductors having a tapered cross-sectionthat corresponds to the taper of the sectors. This type of cross-sectionmaximizes the density of the conductor in the gap between axiallyadjacent poles and, thus, the current capacity of the conductor. Thecross-sectional shape may be rectangular to further maximize conductordensity.

The terms "rotor" and "stator," as defined herein, are used for purposesof convenience to mean only that the rotor and stator rotate withrespect to one another. The terms are not intended to limit theinvention to a structure in which the rotor rotates and the stator isstationary with respect to the earth or other frame of reference. Forexample, the rotor may be fixedly connected to a vehicle body, and thestator may be fixedly connected at its periphery to a tire, whereby therotation of the stator and its tire relative to the rotor and thevehicle body propels the vehicle.

Although the magnets do not have as high a magnetic flux density ("B")as rare earth magnets and other high-permeability magnets, they have ahigher maximum energy product. Energy product is the product of fluxdensity and magnetization force or coercivity ("H") at the point alongthe magnet's characteristic B-H plot at which the motor/generator isoperating. The magnets are thus preferably spaced apart from one anotherby a distance corresponding to the maximum energy product.

The inclusion of three or more rotor magnets in the manner describedabove more than offsets the negative effect of lower flux density onmotor efficiency. Each point or magnetic domain within each centermagnet, i.e., a magnet other than the two outer magnets, contributesequally to the magnetic flux through which the stator conductors pass.Flux emanating from domains immediately to either side of the midplaneof a center magnet thus has a shorter gap to traverse than fluxemanating from corresponding domains in a conventional axial fieldmotor. In other words, both "sides" of each center magnet contribute tothe total flux interacting with a stator conductor. Using both sides ofthe magnet in this manner produces a high average energy product.

Each layer of the stator may be removably connectable to another layerto provide modularity in manufacturing and to facilitate selection ofthe voltage at which the motor/generator is to operate. Each layer mayinclude a casing in which the conductors are enclosed or embedded.Electrical contacts, such as pins extending from the casing, removablyconnect the conductors of adjacent layers. Because voltage is dependentupon the length of a conductor that passes through a magnetic field,selecting the total conductor length of each phase selects the voltage.The pins or other electrical contacts may be disposed around the casingin a manner that allows a user or manufacturer to select the operatingvoltage of the motor/generator by connecting adjacent layers in aselected angular orientation with respect to each another. If the useror manufacturer selects an orientation in which the conductors ofadjacent layers are electrically connected in parallel, the operatingvoltage will be lower than if the user or manufacturer selects anorientation in which the conductors of adjacent layers are electricallyconnected in series. Thus, the user or manufacturer may connect thecasings in various combinations of angular orientations to select one ofa number of voltages at which the motor/generator is to operate, such as120 volts, 240 volts and 480 volts. The exteriors of the casings may bemarked with indicia that facilitate the selection of an operatingvoltage by aligning the indicia and then connecting the casings via thepins.

The present invention also includes a novel method that may be used tomount the magnets during manufacture of the motor. In accordance withthis method, a magnet is dynamically balanced on the shaft on which itis mounted by hardening a thin ring of liquid material between themagnet and the shaft (or a hub mounted to the shaft) while the shaft isspun. The material may be, for example, a polymer resin that iscross-linked and thus hardened by exposure to ultraviolet light whilethe shaft is spun.

The foregoing, together with other features and advantages of thepresent invention, will become more apparent when referring to thefollowing specification, claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following detailed description of the embodimentsillustrated in the accompanying drawings, wherein:

FIG. 1 is a pictorial view of an exemplary motor/generator of thepresent invention;

FIG. 2 is an enlarged sectional view taken on line 2--2 of FIG. 1;

FIG. 3 is a sectional view taken on line 3--3 of FIG. 2;

FIG. 4 is a face view of a rotor of the motor/generator, showing thepolarization of the magnet;

FIG. 5 is a side elevation view of a rotor;

FIG. 6 is a graphical illustration of the magnetic flux emanating from arotor;

FIG. 7 is a plot of magnetic flux of the magnetic flux versus thecoercivity of a magnet;

FIG. 8 is a plot similar to FIG. 9, showing magnetic flux versuscoercivity of a magnet of the motor/generator;

FIG. 9 is a pictorial view of a method for assembling a rotor bymounting a magnet on a hub;

FIG. 10 is a pictorial view of a method for curing the material thatadheres the magnet to the hub;

FIG. 11 is a pictorial view of a stator of the motor/generator;

FIG. 12 illustrates a stator winding arrangement having multiple turnsof wire conductors;

FIG. 13 is a schematic diagram of the stator winding arrangement;

FIG. 14 is a pictorial view of an alternative stator winding arrangementhaving single-turn, rectangular cross-section conductors;

FIG. 15 is a flux diagram of the rotor;

FIG. 16 is a top plan view of a portion of another alternative statorwinding arrangement having multiple laminations of two-sided, flexible,printed circuit material, showing the portion of the stator windingarrangement relating to one phase of windings of one of the laminations;

FIG. 17 is a top plan view similar to FIG. 15, but illustrating bothsides of one of the laminations;

FIG. 18 is a sectional view taken along line 18--18 of FIG. 17, showingthe multiple laminations;

FIG. 19 is a sectional view taken along line 19--19 of FIG. 17;

FIG. 20 is a partial top plan view similar to FIG. 17, but showing theportion of the stator winding arrangement relating to 12 phases ofwindings of one of the laminations;

FIG. 21 is a block diagram of a motor controller;

FIG. 22 is a timing diagram of the motor signals;

FIG. 23 is a schematic diagram of the stators connected to one anotherin a configuration selected to operate the motor/generator at a firstvoltage;

FIG. 24 is a schematic diagram of the stators connected to one anotherin a configuration selected to operate the motor/generator at a secondvoltage;

FIG. 25 is a schematic diagram of the stators connected in aconfiguration selected to operate the motor/generator at a thirdvoltage; and

FIG. 26 is, in part, a front elevation view of a vehicle having themotor/generator disposed within a wheel and, in part, a cross-sectionaldetail view of an alternative embodiment of the motor/generator suitablefor installation within the wheel.

DESCRIPTION OF PREFERRED EMBODIMENTS

As illustrated in FIGS. 1-3, a motor/generator includes a housing 10(the center section of which is shown removed), multiple layers orstator assemblies 12 connected to one another and disposed withinhousing 10, and a rotor having multiple rotor discs 14 and 15 connectedto a shaft 16 that extends axially through housing 10. Housing 10includes two endpieces 18 and 20, each having multiple housingventilation openings 22. Housing 10 also includes at least one removablemidsection piece between endpieces 18 and 20 that is indicated inphantom line in FIGS. 1-3 but not shown for purposes of clarity.Endpieces 18 and 20 and the removable midsection pieces are preferablymade of light-weight plastic. Bolts 24 extend from endpiece 18 axiallythrough housing 10 through each stator assembly 12 and are secured bynuts 26 at endpiece 20. At one end of housing 20, ball bearings 28retained between a first bearing race 30 connected to shaft 16 and asecond bearing race 32 connected to endpiece 18 facilitate rotation ofshaft 16 with respect to housing 10. A similar bearing arrangementhaving ball bearings 34 retained between a first bearing race 36connected to shaft 16 and a second bearing race 38 connected to endpiece20 facilitate rotation of shaft 16 at the other end of housing 10.

1. Modular Construction of the Motor/Generator

Rotor discs 14 and 15 are interleaved with stator assemblies 12.Although stator assemblies 12 are described in further detail below, itshould be noted that stator assemblies 12 are removably connectable toone another. A motor/generator having any selected number of statorassemblies 12 may be constructed. Stated another way, themotor/generator has a stator comprising a selected number of layers.Preferably, for reasons discussed below, the motor/generator has atleast two stator assemblies 12 and three rotor disks 14. Removable pins40 plug into sockets 42 to electrically connect each stator assembly 12to an adjacent stator assembly 12. Electrical power leads 44 extend intohousing 10 and have plugs 46 that connect to sockets 42 in one of thetwo endmost stator assemblies 12. Although FIG. 3 illustrates a powerlead 44 connected to the endmost stator assembly 12 adjacent endpiece20, it could alternatively be connected to the endmost stator assembly12 adjacent endpiece 18. As illustrated in FIGS. 1 and 3, openings orports 48 and 50 in endpieces 18 and 20, respectively, admit plugs 46into housing 10. A sensor 52, which is preferably a Hall-effect sensor,is mounted to endpiece 20. Sensor 52 is adjacent the endmost rotor disc14 for sensing pole transitions, as described below with respect to theoperation of the motor/generator.

2. The Rotor

As illustrated in FIGS. 2 and 4, each rotor disc 14 an 15 includes anannular ceramic magnet 54 mounted on a hub 56. Hub 56 has hubventilation openings 58 with angled, vane-like walls for impellingcooling air through housing 10. Magnets 54 may be made from a suitableferroceramic material, such as M-V through M-VIII, oriented bariumferrite (BaO--6Fe₆ --O₂), strontium ferrite (SrO--6Fe₆ --O₂), or leadferrite (PbO--6Fe₆ --O₂). Alternatively, magnets 54 may be made from abonded neodymium material. Such materials have the added advantage ofbeing much lighter than rare earth and iron magnetic materials. Bothferroceramic magnets and bonded neodymium magnets are known in the artand commercially available. As illustrated in FIG. 4, each magnet 54 ispolarized to provide multiple sectors 57 uniformly distributed angularlyaround magnet 54. As illustrated in FIG. 5, each sector is polarizedthrough the thickness of magnet 54. Thus, each sector has opposite poleson opposite faces 60 and 62 of the magnet 54. In addition, the poles ofsectors 57 on face 60 alternate with those of adjacent sectors 57 onface 60, and the poles of sectors 57 on face 62 alternate with those ofadjacent sectors on face 62. Each rotor disc 14 is mounted on shaft 16with the poles of its magnet 54 axially aligned with opposite poles ofan adjacent magnet 54 (i.e., a North pole on face 62 of a first rotormagnet 54 will be axially aligned with a South pole on face 60 of asecond adjacent rotor magnet 54). Magnetic flux therefore exists betweensuch axially aligned poles. As illustrated in FIGS. 3 and 15, annulardiscs or endplates 64 and 66, made of a suitable high-permeabilitymaterial such as steel, are mounted to faces 60 of the magnets 54 of theendmost two rotor discs 14. Endplates 64 and 66 contain the magneticflux between adjacent poles of the rotor magnet 54 adjacent to endplate64 or 66.

As illustrated in FIG. 15, conceptually, the magnetic flux "flows" froma sector 57 of a first one of the two endmost magnets 54, throughaxially aligned sectors 57 of adjacent magnets 54 until reaching thesecond one of the two magnets 54 of an endmost rotor disc 14, where oneof endplates 64 and 66 directs the flux to an angularly adjacent sector57. The flux then returns axially through aligned sectors 57 of adjacentmagnets 54 until again reaching the first magnet 54 of an endmost rotordisc 14, where the other of endplates 64 and 66 directs the flux to anangularly adjacent sector 57. The magnets 54 other than the two magnets54 of an endmost rotor disc 14, may be referred to herein forconvenience as inner or center magnets. The flux thus follows aserpentine pattern, weaving axially back and forth through alignedsectors 57 of magnets 54 of the center rotor discs 15 and endmost rotordiscs 14.

As noted above, the motor/generator should have at least one inner orcenter rotor disc 15 and two outer or endmost rotor disc 14, each havinga magnet 54. Nevertheless, the greater the number of center rotor disc15, the greater the ratio of total flux density to total weight of themotor/generator and, correspondingly, the greater the power-to-weightratio of the motor/generator. Therefore, the motor/generator preferablyhas at least three or four center rotor discs 15 and can achieve apower-to-weight ratio of between about 0.1 and 1.0 horsepower per pound(HP/lb.), with a typical power-to-weight ratio of about 0.5 HP/lb. Withthis number of center rotor discs 15 it can achieve an efficiencybetween about 88 percent and 99 percent, with a typical efficiencybetween 92 and 96 percent. The motor/generator can achieve the high fluxdensity-to-weight ratio because essentially every point or magneticdomain within each center rotor disc 15 contributes to the total flux.Conceptually, flux emanating from a domain midway between faces 60 and62 (FIG. 15 ) of a center rotor disc 15 impinges equally upon bothadjacent stator assemblies 12. In a conventional axial field motor, theflux emanating from each magnet is directed to only one stator winding.Thus, in the conventional axial field motor, the domains closer to thewinding contribute more flux than the domains farther from the winding.

Magnets 54 have more than two poles to minimize demagnetization beforethey are assembled into the rotor. The greater the number of poles, theless demagnetization a magnet 54 will experience because the length ofthe flux lines between adjacent poles will be minimized. While it isdifficult if not impossible to create pole transitions inhigh-permeability material, e.g., iron, steel, Alnico andsamarium-cobalt materials, which have permeabilities thousands of timesthat of air, pole transitions are readily created in low-permeabilitymaterials, such as ferroceramic and bonded neodymium materials, whichhaving permeabilities on the order of that of air. Nevertheless, anymaterial having a permeability no more than about 100 times that of airwould be suitable for magnets 54. As illustrated in FIG. 6, the fluxdensity (B) curve 68 transitions sharply at the midpoint 70 betweenpoles of a magnet 54. In contrast, the flux density (B) curve 72 of ahigh-permeability magnet (not shown) would transition very gradually,thereby defining poles that are less distinct than those of aferroceramic magnet. The transition area, "d", is defined as the area inwhich the magnetic flux emanating from a pole returns to a laterallyadjacent pole on the same magnet 54 rather than travels to an axiallyadjacent pole of an axially adjacent magnet 54.

The number of poles in magnets 54 and the spacing between magnets 54along rotor shaft 16 (see FIG. 15 ) is preferably determined in responseto the magnetization characteristics of the ceramic material. Asillustrated in FIG. 7, an exemplary characteristic curve, sometimesreferred to as a "B-H curve" 74, is defined by a plot of flux density(B) versus coercivity (H) of magnet 54. A similar B-H exemplary curve 76for a high-permeability magnet is shown for comparison. It should benoted that curves 74 and 76 each include two relatively flat portions ofdiffering slopes connected at a "knee."

As illustrated in FIG. 15 , and with reference to FIG. 8, the spacing 77between adjacent magnets 54 on rotor shaft 16 is preferably selected tomaximize the energy product 78, which is defined as the product of fluxdensity and coercivity at a point on B-H curve 74. (Flux density,expressed in units of Gauss, multiplied by coercivity, expressed inunits of Oersteds, is equal to energy, expressed in units of Joules.)Energy product 78 is maximized when magnets 54 operate at exemplarypoint 80 on B-H curve 74. Because the demagnetizing force or coercivity(H) of a magnet 54 is proportional to spacing 77, and the flux density(B) of a magnet 54 is proportional to its thickness, spacing 77 of amagnet 54 operating at point 80 can be calculated by dividing thethickness of magnet 54 by the slope of B-H curve 74 at the portion ofthe curve near the B axis that is relatively flat. For the preferredferroceramic materials, the slope at this portion of their B-H curve isapproximately equal to one; thus, energy product 78 is maximized whenmagnets 54 are spaced by a distance equal to their thickness.

Spacing 77 can also be described in relation to the width of thetransition zone (d) between adjacent poles of a magnet 54. (See FIG. 6).As described above, in the transition zone, magnetic flux emanating froma pole returns to an adjacent pole on the same magnet 54 and does nottravel to a pole of an adjacent magnet 54, because the length of eachflux line in the transition zone is shorter than the axial distancebetween that point and a point on an adjacent magnet 54. Thus, thelength of a flux line spanning the transition zone is essentially equalto spacing 77. Because flux lines returning to an adjacent pole of thesame magnet 54 are essentially semicircular in air, the length of a fluxline spanning the transition zone is equal to one-half the circumferenceof a circle having a diameter that is the width of the transition zone.Therefore, the width of the transition zone is twice spacing 77 dividedby pi(π).

As illustrated in FIG. 4, and with reference to FIG. 8, the number ofsectors 57 (or, equivalently, the number of poles) is preferablyselected to operate magnets 54 exactly at the knee of their B-H curve74, indicated by point 82, prior to assembling magnets 54 into therotor. Because the demagnetizing force or coercivity (H) of a magnet 54is proportional to the length of its longest flux lines, and the fluxdensity (B) of a magnet 54 is proportional to its thickness, the lengthof the longest flux lines 81 of a magnet 54 operating at point 82 can becalculated by determining the slope of a diagonal 83 of a box having acorner at point 82, and then dividing the thickness of magnet 54 by thisslope. The longest flux lines 81 extend between points substantially atthe centers of adjacent sectors 57 at the outer peripheries of sectors57. Because flux lines returning to an adjacent pole of the same magnet54 are essentially semicircular in air, the distance or chord betweensuch center points is equal to twice the length of the longest fluxlines 81 divided by pi (π). (Viewed from the top, as in the plan view ofFIG. 4, the longest flux lines 81 appear coextensive with such chords.)The angle 85 subtended by such a chord divided into 360 degrees is equalto the preferred number of sectors 57. The exemplary magnet 54 shown inFIG. 8 has eight sectors 57, each subtending an angle of 45 degrees.

By operating magnets 54 at the knee prior to assembly, the flux betweeneach pole of a magnet 54 and the axially aligned pole of an adjacentmagnet 54 is maximized when the rotor is assembled. A greater number ofpoles would increase the flux density between the angularly adjacentpoles of a magnet 54 and correspondingly decrease the flux betweenaxially adjacent magnets 54. A lesser number of poles would move theoperating point beyond the knee to, for example, point 84. Once theoperating point of a magnet has moved beyond the knee of itscharacteristic B-H curve, it becomes permanently demagnetized to someextent and thereafter operates on a minor B-H curve 86.

As illustrated in FIG. 9, a novel method may be used to mount magnets 54to a hubs 56. As those of skill in the art will appreciate, annularceramic magnets typically are not precisely uniform as a result of thecasting and kilning method by which they are made. Thus, their centersof gravity are typically not located precisely at their centers. It istherefore desirable to balance each magnet 54 to minimize vibration andmechanical stresses during operation of the motor/generator.Nevertheless, it would be difficult to balance magnets 54 by removingmaterial from them because ceramic materials are difficult to machine.It would also be difficult to balance magnets 54 by attaching weights orbands to their peripheries due to the differential thermal expansionbetween the ceramic and the weights. In accordance with the novelmethod, hub 56 is removably mounted on a shaft 88 connected to a motor90. Cross-linkable polymer resin, such as the well-known type that iscommercially available for dental repair, is applied to either the outerrim 92 of hub 56, the inner rim 94 of magnet 54, or both. Magnet 54 isthen fit onto hub 56. Motor 90 is energized to slowly increase itsspeed. Hub 56 rotates magnet 54 because the relatively high viscosity ofthe resin creates sufficient friction or adhesion between them. Therotation dynamically balances magnet 54 on hub 56 because the resinflows and redistributes itself in the space between hub 56 and magnet54. As illustrated in FIG. 10, when magnet 54 is rotating smoothly withno noticeable vibration, an ultraviolet lamp 96 is energized toilluminate the resin. As is well-known in the art, ultraviolet lightcross-links the polymer molecules and thereby hardens the resin. Magnet54 remains balanced while the resin hardens because it remains spinningwith hub 56. When the resin is sufficiently hardened, lamp 76 and motor70 are de-energized. The resulting rotor disc 14, comprising magnet 54adhered to hub 56 by a layer of hardened resin 98, is then removed fromshaft 68.

3. The Stator

As described above, the stator of the motor/generator includes multiplestator assemblies 12. As best illustrated in FIGS. 3, 11 and 12, oneembodiment of a stator assembly 12 includes windings 100 around adielectric form 102 that is embedded, molded or similarly encased in asubstantially annular stator casing 104 made of a suitable dielectricmaterial. Stator assembly 12 has bores 106 through which bolts 24 may beextended to physically interconnect them, as described above withrespect to FIGS. 1 and 2. As similarly described above, stator assembly12 has sockets 42 that may be electrically interconnected by removablepins 40. Stator casing 104 has a central opening 108 through which shaft16 extends when the motor/generator is assembled, as illustrated in FIG.2. The diameter of shaft 16 is less than that of central opening 108 tofacilitate airflow through the motor/generator.

As illustrated in FIG. 13, the exemplary motor/generator has fourphases, designated phase-1 (φ₁), phase-2 (φ₂), phase-3 (φ₃) and phase-4(φ₄). Each phase is defined by a conductor phase assembly, comprising alength of a suitable conductor 110, 112, 114 and 116, respectively, suchas dielectric-coated copper or aluminum magnet wire of a suitable gauge,electrically connected at each end to a socket 42. For example,conductor 110 is connected between a socket 42, designated phase-1positive (φ₁ +) and a socket 42 designated phase-1 negative (φ₁ -).

Although a motor/generator having four phases is illustrated, the numberof phases is preferably selected in response to the length of thetransition area between the poles of magnet 54. Referring briefly toFIG. 6, the motor/generator preferably has a number of phases equal tothe length ("L") of the outer periphery of a sector 57 divided by thelength ("d") of the transition area. The number of phases is, in effect,the number of transition areas that fit within a sector 57. If magnets54 are spaced by the preferred distance of twice the length ("d") of thetransition zone between poles, as described above with respect to FIG.6, the preferred number of phases is: ##EQU1## where "2πr" is thecircumference of magnet 54, and "N" is the number of sectors 57.

Each conductor phase assembly includes eight windings 100 distributedaround form 102. As defined herein, the term "winding" broadly refers toa conductor having at least one portion oriented or elongated in adirection that traverses or cuts the flux lines when the motor/generatoris in operation. FIG. 13 illustrates windings 100 having one suchelongated conductor portion 118 that extends from the periphery of theconductor phase assembly toward the interior of the conductor phaseassembly and another such elongated conductor portion 119 that returnsfrom the interior of the conductor phase assembly to the periphery.Nevertheless, each winding 100 preferably comprises at least two turns.As used herein, a "turn" is defined as a portion of a conductor thatextends from the periphery of the conductor phase assembly toward theinterior and returns from the interior to the periphery. As those ofskill in the art will understand, the number of turns depends upon theselected voltage and current operating parameters. For purposes ofclarity, however, two of the turns of each winding 100 of conductor 110are shown in FIG. 12.

Form 102 has 32 sector-shaped or wedge-shaped partitions 120. Each groupof four adjacent partitions 120 corresponds in size to a sector 57 ofmagnet 54 (FIG. 4). The turns of each winding 100 are wound around sucha group of four adjacent partitions 120, and then an equal number ofturns are wound around an adjacent group of four adjacent partitions120. In this manner, the conductor is wound around each of eight groupsof four partitions 120. Each of conductors 110, 112, 114 and 116 iswound in this manner. The windings of conductor 110 are offset by onepartition 120 from the windings of conductor 112; the windings ofconductor 112 are offset by one partition 120 from the windings ofconductor 114; and the windings of conductor 114 are offset by onepartition 120 from the windings of conductor 116. The completed fourphases of windings define a generally planar or wheel-like structure onthe surface of form 102, with a total of 32 elongated conductor portions118 and 119, each consisting of a bunch or group of wires, arranged in aspoke-like manner.

As illustrated in FIG. 14, in an alternative embodiment, each of fourdielectric-coated conductors 122, 124, 126 and 128, defining phases 1-4,respectively, has a rectangular cross-sectional shape. Thus, thecross-section of each of conductors 122, 124, 126 and 128 has a widthand a thickness. Although in both this embodiment and the embodimentdescribed above, the windings are electrically connected in the mannerschematically illustrated in FIG. 13, in this embodiment the windingsare also physically arranged in a manner similar to that illustrated inFIG. 13. In other words, each of conductors 122, 124, 126 and 128 haseight windings, each having exactly one turn, and each offset from anadjacent winding by four conductor widths. The windings of conductor 122are offset by one conductor width from the windings of conductor 124;the windings of conductor 124 are offset by one conductor width from thewindings of conductor 126; and the windings of conductor 126 are offsetby one conductor width from the windings of conductor 128. Thearrangement is thus analogous to that of the embodiment described above.The four phases of windings define a generally planar or wheel-likestructure, with a total of 32 elongated conductor portions arranged in aspoke-like manner.

The elongated portions of conductors 122, 124, 126 and 128 are taperedor wedge-shaped, i.e., their widths decrease in a radially inwarddirection, thereby allowing them to be packed closely together in thespoke-like arrangement. Conductors 122, 124, 126 and 128 are preferablymade of metal cast or otherwise formed into the illustrated windingshape, but it may also be suitable to wind rectangular or square taperedmetal wire into the illustrated winding shape. Packing conductors 122,124, 126 and 128 closely together maximizes the amount of theirconductive material that passes through the flux. The ratio of thisamount to the total amount of conductive material in the windings of amotor/generator is commonly known as the "fill factor." The fill factorfor the stator shown in FIG. 14 is greater than 80 percent. Although thelengths of conductors 122, 124, 126 and 128 are less than the lengths ofconductors 110, 112, 114 and 116 in the embodiment described withrespect to FIG. 12, the fill factor is much greater in this embodiment.Furthermore, although the cross-sectional area of the wedge-shapedelongated portions of conductors 122, 124, 126 and 128 varies, theaverage cross-sectional area determines the current capacity. Thus, theminimum width of conductors 122, 124, 126 and 128 does not directlylimit their current capacity.

In another alternative embodiment of the stator, each stator assemblycomprises multiple layers or laminations, each preferably formed ofprinted circuit material that has been suitably etched to form theconductor pattern and electrical interconnections between layersdescribed below. The printed circuit material and etching process may beany such material and process known in the art that is commonly used tomanufacture printed circuit boards or flexible printed circuits in theelectronics industry. The laminations or layers are bonded together orotherwise attached to one another. The resulting multiple-layer printedcircuit stator assembly functions in the same manner as stator assembly12, described above with respect to other embodiments. In that regard,this alternative stator assembly may have any suitable number of phasesand any suitable number of windings per phase. The alternative statorassembly may have a thickness as small as about 0.1 inches, therebyfacilitating the construction of smaller motor/generators. Nevertheless,a typical alternative stator assembly for a small motor may have athickness of about 0.25 inches. Larger motors may be constructed usingan alternative stator assembly having a thickness as great as about twoinches.

As illustrated in FIG. 16, each layer or lamination of the alternativestator assembly comprises a substrate 129 made of a suitable dielectricmaterial and multiple arms 131 made of metal that remains following theetching or other manufacturing process. The ellipsis (". . . ") betweenarms 131 indicates that additional arms 131 are included, as describedbelow, but are not shown in FIG. 16 for purposes of clarity. A preferredprinted circuit material is a flexible plastic material, commonlyreferred to as "flex PC," in which substrate 129 is a thin sheet-likeplastic to which is bonded a thin layer of copper. Substrate 129 ispreferably less than about 0.010 inches (10 mils) thick, and arms 131are preferably less than about 0.005 inches (five mils) thick. Printedcircuit material having a four mil copper layer has been used. Thepattern of arms 131 is formed using photolithographic methods well-knownin the printed circuit board fabrication industry. Each arm 131 isoriented in a substantially radial direction with respect to an axis 133normal to substrate 129. Each arm 131 has an elongated conductor portion135 that is oriented in a radial direction so that a current is inducedas it moves through the lines of magnetic flux when the motor/generatoris assembled.

As illustrated in FIGS. 17 and 18, each layer or lamination preferablyhas arms on both sides, in the manner associated with what is commonlyknown as a two-sided printed circuit board. In FIG. 17, arms 131 on thefirst side are shown in solid line, and arms 137 on the second side areshown in broken line. Arms 131 and 137 are essentially identical,mirroring one another in size and position. Each end of an arm 131 iselectrically connected to an end of an arm 137 via an inter-sidethrough-hole 139. Each inter-side through-hole 139 is plated on itsinterior to provide a conductive path in the manner well-known inmulti-layer printed circuit board manufacture.

A first terminal through-hole 141 is disposed at one end of one of arms131, and a second terminal through-hole 143 is disposed at one end ofanother of arms 131. Terminal through-holes 141 and 143 are platedthrough-holes similar to inter-side through-holes 139, but they do notconnect an arm 131 to an arm 137. Rather, terminal through-holes 141 and143 form the terminals of an electrical circuit. That electrical circuitis the conductor phase assembly or at least a portion of it. It shouldbe noted that the conductor path of the circuit, a portion of which isindicated by arrows 145 in FIG. 17, begins at terminal 141, follows oneof arms 131 on the first side of the lamination, changes sides via oneof inter-side through-holes 139, and continues through one of arms 137on the second side of the lamination. The portion of the conductor pathindicated by arrows 145 defines a winding. (The winding has only asingle turn of conductor, in a manner similar to the embodimentdescribed above with respect to FIG. 14.) The circuit then follows asecond winding by again changing sides via another of inter-sidethrough-holes 139, and continues through another of arms 131. Thecircuit shown in FIG. 17 thus includes six such windings on each side ofthe lamination.

Although a conductor phase assembly may consist of only the windings ofa single lamination, such as that shown in FIG. 17, a conductor phaseassembly preferably includes windings of multiple laminationselectrically connected in parallel. As illustrated in FIG. 18, thelaminations are bonded together to form a stator assembly. A plasticsheet 147 between laminations bonds the laminations together when heatedand subjected to pressure, and also electrically insulates arms 137 ofone lamination from arms 131 of an adjacent lamination. As illustratedin FIG. 19, terminal through-holes 141 of all laminations areelectrically connected together, and terminal through-holes 143 of alllaminations are electrically connected together, thereby electricallyconnecting the windings in parallel to form a conductor phase assembly.

As illustrated in FIG. 20, the stator assembly preferably includesmultiple conductor phase assemblies. The embodiment illustrated in FIG.20 includes 12 conductor phase assemblies, thereby providing a 12-phasestator assembly. In a 12-phase stator assembly, arms 131 and 137 arearranged at an angular spacing of 2.5 degrees. For purposes of clarity,only a portion of the stator assembly is shown in FIG. 20, illustratingthe pair of terminals for phase-1, labeled "φ₁ ⁺ " and "φ₁ ⁻ ", and thepair of terminals for phase-2, labeled "φ₂ ⁺ " and "φ₂ ⁻ ".Nevertheless, the complete stator assembly has 12 pairs of terminals forphases 1-12. To electrically insulate them, arms 131 are separated fromone another, and arms 137 are separated from one another, by a smallspacing, which is not shown as such in FIG. 20, but rather isrepresented by the boundary line between adjacent arms 131 and 137 forpurposes of clarity.

In view of the embodiments illustrated in FIGS. 12, 14 and 16-20,persons of skill in the art will understand that in other embodimentsthe conductors may have any suitable size, shape, and number of windingsand turns. For example, in an embodiment similar to that illustrated inFIG. 14, each winding may have two turns of rectangular wire havingwedge-shaped elongated portions. A conductor may range in size amongvarious embodiments from, for example, a thin printed circuit trace to athick metal casting.

4. Controlling the Motor/Generator

As illustrated in FIG. 21, the motor/generator may be configured as amotor by connecting a brushless motor controller 130 of essentiallyconventional design. Brushless motor controller 130 receives a polesense signal 132 from sensor 52 (FIG. 3) and generates signals 134 (φ₁-), 136 (φ₁ +), 138 (φ₂ -), 140 (φ₂ +), 142 (φ₃ -), 144 (φ₃ +), 146 (φ₄-) and 148 (φ₄ +). Signals 134, 136, 138, 140, 142, 144, 146 and 148 arecoupled to electrical leads 44, as described above with respect to FIG.2.

As illustrated in the timing diagram of FIG. 22, the differentialvoltage between signals 134 and 136 defines a series of phase-1 pulses150; the differential voltage between signals 138 and 140 defines aseries of phase-2 pulses 152; the differential voltage between signals142 and 144 defines a series of phase-3 pulses 154; and the differentialvoltage between signals 146 and 148 defines a series of phase-4 pulses156. Brushless motor controller 130 may select the width of pulses 150,152, 154 and 156 to provide suitable motor torque. Brushless motorcontroller 130 sequentially generates one of pulses 150, 152, 154 and156. Brushless motor controller 130 repeats this sequence until itreceives pole sense signal 132, which indicates that magnets 54 haverotated one pole. At that point, brushless motor controller 130 reversesthe voltages of pulses 150, 152, 154 and 156 but continues generatingthem in the same sequence.

5. Voltage Selection

The modular construction of the motor/generator facilitates selection ofan operating voltage. Operating voltage is proportional to the totalconductor length for each phase. Thus, an operating voltage may beselected by adjusting the total conductor length for each phase. Eachstator assembly 12 has conductors 110, 112, 114 and 116, each definingone of the four phases. (See, e.g., FIG. 13.) By connecting, forexample, conductor 110 in each stator assembly 12 in parallel withconductor 110 in all other stator assemblies 12, the total conductorlength for phase-1 is minimized. Conversely, by connecting, for example,conductor 110 in each stator assembly 12 in series with conductor 110 inall other stator assemblies 12, the total conductor length for phase-1is maximized. The modular construction facilitates selectably connectingthe conductors of adjacent stator assemblies in either series orparallel.

As illustrated in FIG. 1, each stator assembly 12 has indicia 158, 160and 162, such as adhesive labels, each indicating one of the voltagesthat may be selected. An operating voltage can be selected by connectingeach stator assembly 12 in an angular orientation in which the indiciaindicating a certain voltage are aligned. Indicia 158 are labeled "120"to indicate 120 volts; indicia 160 are labeled "240" to indicate 240volts; and indicia 162 are labeled "480" to indicate 480 volts. In theexemplary relative angular orientation of stator assemblies 12 shown inFIG. 1, indicia 158 are aligned to select an operating voltage of 120volts. To change the operating voltage, one need only uncouple one ormore stator assemblies 12 and rotate them to realign indicia 158 suchthat they align to indicate a different operating voltage.

As illustrated schematically in FIG. 23, stator assemblies 12 areinterconnected to select a first operating voltage, such as 120 volts.Broken lines indicate an electrical connection. With respect to phase-1,each end of conductor 110 in each stator assembly 12 is connected by aremovable pin 40 to the corresponding end of conductor 110 in anotherstator assembly 12. Thus, all conductors 110 are connected in parallel.Similarly, with respect to phase-2, each end of conductor 112 in eachstator assembly 12 is connected by a removable pin 40 to thecorresponding end of conductor 112 in another stator assembly 12. Thus,all conductors 112 are connected in parallel. All conductors 114 and 116are similarly connected in parallel. Pins 40 at one of the endmoststator assemblies 12 may be connected to electrical power leads 44 (FIG.1). It should be noted that all indicia 158 are aligned, but indicia 160and indicia 162 are not aligned.

As illustrated schematically in FIG. 24, stator assemblies 12 areinterconnected to select a second operating voltage, such as 480 volts.As in FIG. 24, broken lines indicate an electrical connection. Withrespect to phase-1, with the exception of the two endmost statorassemblies 12, a first end of conductor 110 in each stator assembly 12is connected by a removable pin 40 to a second end of conductor 110 inanother stator assembly 12. Thus, all conductors 110 are connected inseries. Similarly, with respect to phase-2, with the exception of thetwo endmost stator assemblies 12, a first end of conductor 112 in eachstator assembly 12 is connected by a removable pin 40 to a second end ofconductor 112 in another stator assembly 12. Thus, all conductors 112are connected in series. All conductors 114 and 116 are similarlyconnected in series. Pins 40 at the endmost stator assemblies 12 may beconnected to electrical power leads 44 (FIG. 1). It should be noted thatall indicia 162 are aligned, but indicia 158 and indicia 160 are notaligned.

As illustrated schematically in FIG. 25, stator assemblies 12 areinterconnected to select a third operating voltage, such as 240 volts.In the same manner as in FIGS. 23 and 24, broken lines indicate anelectrical connection. With respect to phase-1, with the exception ofthe two endmost stator assemblies 12, the corresponding first and secondends of conductors 110 in two adjacent stator assemblies 12 areconnected to each other by a removable pin 40; a first end of conductor110 in one of those stator assemblies 12 is connected by a removable pin40 to a second end of conductor 110 in a third stator assembly 12; andthe corresponding first and second ends of conductors 110 in the thirdstator assembly 12 and an adjacent fourth stator assembly 12 areconnected to each other by a removable pin 40. Thus, groups of twoconductors 110 are connected in parallel, and the groups are connectedin series. Similarly, with respect to phase-2, with the exception of thetwo endmost stator assemblies 12, the corresponding first and secondends of conductors 112 in two adjacent stator assemblies 12 areconnected to each other by a removable pin 40; a first end of conductor112 in one of those stator assemblies 12 is connected by a removable pin40 to a second end of conductor 112 in a third stator assembly 12; andthe corresponding first and second ends of conductors 112 in the thirdstator assembly 12 and an adjacent fourth stator assembly 12 areconnected to each other by a removable pin 40. Thus, groups of twoconductors 112 are connected in parallel, and the groups are connectedin series. All conductors 114 and 116 are similarly connected inparallel groups of two that are connected in series. Pins 40 at theendmost stator assemblies 12 may be connected to electrical power leads44 (FIG. 1). It should be noted that all indicia 160 are aligned, butindicia 158 and indicia 162 are not aligned.

As persons of skill in the art will appreciate, the conductors may beinterconnected in various combinations of series and parallel groups toprovide more than three selectable voltages. Moreover, the illustratedset of voltages is exemplary only; in view of the teachings herein,persons of skill in the art will readily be capable of constructing amotor/generator operable at other voltages.

6. Conclusion

The motor/generator has a modular construction and a highpower-to-weight ratio because no metal casing is required to contain themagnetic field. The field has a serpentine shape and is contained withinthe rotor structure by the magnets 54 themselves and two relativelysmall endplates 64 and 66.

The magnets 54 are polarized into a number of sectors 57 to minimizedemagnetization prior to assembly of the rotor. Thus, the magnets 54 maybe magnetized prior to assembly and maintained in inventory by themanufacturer. No keeper need be used to maintain the magnetization.Similarly, the rotor may be removed from the motor/generator to select adifferent operating voltage without substantially demagnetizing themagnets 54.

The modular construction facilitates voltage selection. To select thevoltage, the orientation of each stator assembly 12 may be selected withrespect to other stator assemblies 12 and then connected to other statorassemblies 12 by removable pins 40. Indicia 158, 160 and 162 on thestator assemblies 12 may aid the user in selecting the orientation.

The motor/generator may be used to power any suitable type of device,machine or vehicle. For example, it may be used in domestic appliancessuch as refrigerators and washing machines. It may also be used to powervehicles such as automobiles, trains and boats. One such use as a powerplant in a vehicle is illustrated in FIG. 26. In the embodimentillustrated in FIG. 25, the motor/generator is mounted in a casing 164that functions as the hub for a traction device such as the rubber tire166 of an automotive vehicle 168. The shaft 170 is fixedly, i.e.,non-rotatably, connected to the body of vehicle 168. The rotor discs172, which are of substantially the same construction as described abovewith respect to other embodiments, are fixedly connected to casing 164and thus rotate with tire 166. The stator assemblies 174 are fixedlyconnected to shaft 170 but are otherwise constructed as described abovewith respect to other embodiments. In operation, the rotation of rotordiscs 172 propels the vehicle while the shaft remains stationary withrespect to the ground.

Obviously, other embodiments and modifications of the present inventionwill occur readily to those of ordinary skill in the art in view ofthese teachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such other embodiments andmodifications when viewed in conjunction with the above specificationand accompanying drawings.

What is claimed is:
 1. A motor/generator, comprising:a stator having anaxis and at least two layers spaced along said axis, each layerincluding a conductor phase assembly with a winding having an elongatedconductor portion oriented in a generally radial direction with respectto said axis; a rotor having an axis coaxial with said axis of saidstator, said rotor comprising:a shaft rotatably coupled to said stator;at least three annular magnets including two annular outer magnets andat least one annular center magnet; said two annular outer magnetscoaxially coupled to said shaft, each outer magnet having apermeability, an axis, first and second faces and a plurality ofcontiguous sector-shaped poles, an axial distance between said facesdefining a thickness, each pole of said first face being of oppositepolarity from an angularly adjacent pole of said first face and ofopposite polarity from an axially adjacent pole of said second face;said annular center magnet coaxially coupled to said shaft between saidouter magnets, each center magnet having a permeability, an axis, firstand second faces and a plurality of contiguous sector-shaped poles, anaxial distance between said faces defining a thickness, each pole ofsaid first face being of opposite polarity from an angularly adjacentpole of said first face and of opposite polarity from an axiallyadjacent pole of said second face; and one of said first and secondfaces of each sector of each magnet having a pole fixedly aligned with apole of an adjacent magnet having opposite polarity; and saidthicknesses of said magnets being substantially equal, each magnet beingaxially spaced from an adjacent magnet by a gap spacing approximatelyequal to said thickness, said winding of each of said layers of saidstator being disposed between axially spaced adjacent magnets; and twoendcaps, each having a permeability greater than said permeability ofsaid outer magnets and disposed adjacent one of said first and secondfaces of an outer magnet.
 2. The motor/generator recited in claim 1,wherein each said conductor phase assembly comprises a plurality ofplanar windings angularly distributed around said axis of said stator.3. The motor/generator recited in claim 2, wherein each winding hasexactly two said elongated conductor portions, said elongated conductorportions angularly spaced from one another by an angular spacing equalto an angular spacing of said poles.
 4. The motor/generator recited inclaim 1, wherein said permeability of each outer and central magnet isno more than 100 times the permeability of air.
 5. The motor/generatorrecited in claim 1, wherein each magnet is made of a ferroceramicmaterial.
 6. The motor/generator recited in claim 1, wherein saidplurality of contiguous sector-shaped poles of each magnet is selectedin number to prevent operation beyond a knee of a characteristic B-Hcurve of said magnet when said magnet is magnetically isolated fromother magnets.
 7. The motor/generator recited in claim 1, wherein:eachsaid magnet has an opening with a circumference, and each said sectorhas an inside length along a portion of said circumference of saidopening; each said magnet has a transition area between poles ofangularly adjacent sectors, said transition area has a transition width,and each layer of said stator includes a number of said conductor phaseassemblies essentially equal to said inside length divided by saidtransition width and multiplied by the number of sectors.
 8. Themotor/generator recited in claim 1, wherein said elongated conductorportion of each conductor phase assembly has a tapering cross-sectionalarea.
 9. The motor/generator recited in claim 8, wherein saidmotor/generator has a fill factor greater than 80 percent.
 10. Themotor/generator recited in claim 8, wherein each said elongatedconductor portion has a rectangular cross-sectional shape.
 11. Themotor/generator recited in claim 1, wherein each elongated conductorportion has a round cross-sectional shape.
 12. The motor/generatorrecited in claim 1, wherein each said layer of said stator comprises aplurality of laminations, each having a planar substrate, and saidwinding comprises a metallic layer bonded to said substrate.
 13. Themotor/generator recited in claim 12, wherein said substrate is made ofsheet-like plastic having a thickness less than about 0.025 inches. 14.The motor/generator recited in claim 13, wherein said winding comprisesa metallic layer having a thickness less than about 0.005 inches. 15.The motor/generator recited in claim 1, wherein each said layer of saidstator comprises a casing having said conductor phase assembly enclosedtherein.
 16. The motor/generator recited in claim 15, wherein each saidcasing is removably connectable to an adjacent casing.
 17. Themotor/generator recited in claim 16, further comprising a pin extendingbetween adjacent casings and electrically connecting said conductorphase assemblies of said adjacent casings.
 18. The motor/generatorrecited in claim 1, wherein said motor/generator operates at anefficiency of between 88 percent and 99 percent.
 19. The motor/generatorrecited in claim 18, wherein each magnet is made of a ferroceramicmaterial.
 20. The motor/generator recited in claim 1, wherein saidmotor/generator has a power-to-weight ratio between about 0.1 to 1.0HP/lb.
 21. The motor/generator recited in claim 20, wherein each magnetis made of a ferroceramic material.
 22. The motor/generator recited inclaim 1, wherein said plurality of contiguous sector-shaped poles ofeach annular magnet is equal in number to said plurality of contiguoussector-shaped poles of each other annular magnet.
 23. Themotor/generator recited in claim 1, wherein each sector-shaped pole ofeach annular magnet is the same size as each other sector-shaped pole ofeach other annular magnet.
 24. The motor/generator recited in claim 1,wherein said rotor has a number of said annular magnets and said statorhas a number of said layers, and said number of annular magnets of saidrotor exceeds said number of layers of said stator by exactly one. 25.The motor/generator recited in claim 1, wherein each annular magnet ismade of a material having the same permeability as each other annularmagnet.
 26. A motor/generator, comprising:a stator having an axis and aplurality of layers spaced along said axis; and a rotor having an axiscoaxial with said stator, said rotor comprising a shaft rotatablycoupled to said stator and having a plurality of annular magnetsproducing magnetic fields distributed around said rotor at a pluralityof angular positions, each field extending axially across at least oneof said layers, a first one of said magnets having a thickness andaxially spaced from an adjacent magnet by a gap spacing approximatelyequal to said thickness.
 27. The motor/generator recited in claim 26,wherein each magnetic field is essentially confined within an axiallyoriented region having a sector-shaped cross-section.
 28. Themotor/generator recited in claim 27, wherein each layer comprises aplurality of conductor phase assemblies.
 29. The motor/generator recitedin claim 27, wherein each layer comprises a plurality of planarwindings.
 30. The motor/generator recited in claim 26, wherein each ofsaid annular magnets has a plurality of contiguous sector-shaped polesequal in number to said plurality of contiguous sector-shaped poles ofeach other annular magnet.
 31. The motor/generator recited in claim 26,wherein each of said annular magnets has a plurality of contiguoussector-shaped poles, each the same size as each other sector-shaped poleof each other annular magnet.
 32. The motor/generator recited in claim26, wherein said rotor has a number of said annular magnets and saidstator has a number of said layers, and said number of annular magnetsof said rotor exceeds said number of layers of said stator by exactlyone.
 33. The motor/generator recited in claim 26, wherein each annularmagnet has a permeability and is made of a material having the samepermeability as each other annular magnet.
 34. The motor/generatorrecited in claim 26, wherein:each annular magnet has a plurality ofsector-shaped poles; each layer of said stator has a winding withexactly two elongated conductor portions; and each elongated conductorportion is spaced from another elongated conductor portion by an angularspacing equal to an angular spacing of said poles.
 35. Themotor/generator recited in claim 26, wherein each annular magnet has apermeability no more than 100 times the permeability of air.
 36. Themotor/generator recited in claim 26, wherein each annular magnet is madeof a ferroceramic material.
 37. The motor/generator recited in claim 26,wherein:each said magnet has a plurality of sector-shaped poles and anopening with a circumference, and each said sector-shaped pole has aninside length along a portion of said circumference of said opening;each said magnet has a transition area between poles of angularlyadjacent sectors, said transition area has a transition width, and eachlayer of said stator includes a number of said conductor phaseassemblies essentially equal to said inside length divided by saidtransition width and multiplied by the number of sector-shaped poles.38. The motor/generator recited in claim 26, wherein each layer of saidstator has an elongated conductor portion with a taperingcross-sectional area.
 39. The motor/generator recited in claim 38,wherein said motor/generator has a fill factor greater than 80 percent.40. The motor/generator recited in claim 38, wherein each said elongatedconductor portion has a rectangular cross-sectional shape.
 41. Themotor/generator recited in claim 26, wherein each said layer of saidstator has a winding and comprises a plurality of laminations, eachlamination having a planar substrate, and said winding comprises ametallic layer bonded to said substrate.
 42. The motor/generator recitedin claim 41, wherein said substrate is made of sheet-like plastic havinga thickness less than about 0.025 inches.
 43. The motor/generatorrecited in claim 42, wherein said winding comprises a metallic layerhaving a thickness less than about 0.005 inches.
 44. The motor/generatorrecited in claim 26, wherein each said layer of said stator comprises acasing and a conductor phase assembly enclosed in said casing.
 45. Themotor/generator recited in claim 44, wherein each said casing isremovably connectable to an adjacent casing.
 46. The motor/generatorrecited in claim 45, further comprising a pin extending between adjacentcasings and electrically connecting said conductor phase assemblies ofsaid adjacent casings.
 47. The motor/generatorrecited in claim 26,wherein said motor/generator operates at an efficiency of between 88percent and 99 percent.
 48. The motor/generatorrecited in claim 26,wherein said motor/generator has a power-to-weight ratio between about0.1 to 1.0 HP/lb.
 49. A motor/generator, comprising:a stator having anaxis and a plurality of layers spaced along said axis; and a rotorhaving an axis coaxial with said stator, said rotor comprising a shaftrotatably coupled to said stator and having a plurality of annularmagnets producing magnetic fields distributed around said rotor at aplurality of angular positions, each field extending axially across atleast one of said layers, each magnet having a thickness substantiallyequal to said thickness of all other said magnets, each magnet axiallyspaced from an adjacent magnet by a gap spacing approximately equal tosaid thickness, said plurality of contiguous sector-shaped poles of eachmagnet is selected in number to prevent operation beyond a knee of acharacteristic B-H curve of said magnet when said magnet is magneticallyisolated from other magnets.